Diffuse correlation spectroscopy.

Abstract

Diffuse Correlation Spectroscopy (DCS) is an emerging optical technique for non-invasive measurement of blood flow and hemodynamic studies in deep tissues of human and animal model. This project aims to study the fundamentals of DCS in three stages: (i) Tissue phantom construction, (ii) Intensity fluctuation measurements to acquire the temporal field autocorrelation function, g1(τ) and (iii) Monte Carlo Simulation of photon propagation in pre-defined, tissue-mimicking geometry. In the making of tissue phantom, titanium (iv) oxide (TiO2) and carbon black were used as a scattering and absorbing agent respectively. While information on scattering properties of TiO2 is readily available, calibration of carbon black absorption properties was done to provide an estimated relationship between its concentration used during phantom construction and the absorption coefficient of the resulting phantom. The main focus of the project is on Monte Carlo Simulation of photons diffusion through a system of pre-defined geometry. In a homogeneous, semi-infinite medium in Brownian motion, it was found that the rate of decay of g1(τ) increases with source-detector separation and the Brownian diffusion coefficient, DB but decreases with an increase in absorption coefficient of the pre-defined medium. In a heterogeneous, semi-infinite medium with dynamic plane layer, it was found that for large source-detector separation, the rate of decay of g1(τ) increases as the thickness of the dynamic layer increases, and decreases with an increase in depth of dynamic layer relative to the surface of the medium. However, for small source-detector separation, the rate of decay of g1(τ) remains unchanged regardless of the thickness and position of the dynamic layer. The Monte Carlo results may be a reference for future FYP students to validate their experimental or clinical results.